Parvovirus B19
Parvovirus B19 is a small single-stranded DNA virus belonging to the family of parvoviruses. It was until the discovery of the human Boca Virus 2005 is the only known human pathogenic virus of the genus Erythrovirus. In 1974 it was discovered by accident by the Australian virologist Yvonne Cossart. Bears his name it after the laboratory specimen No. B19, in which it was found. It has a diameter of only 20 to 24 nm, making it one of the smallest known viruses.
Morphology
The virion consists of an icosahedral capsid consisting of multiples of two different viral proteins (VP1 and VP2) is composed. This capsid encloses a linear, single-stranded DNA. The DNA another viral protein is covalently bound. The capsid, the DNA packaged often incomplete, so that a part of the DNA thread protrudes out of the capsid. The virion of parvovirus B19 is characterized by a very high stability against environmental factors and detergents.
The viral genome has a size of 5000 to 5500 nucleotides. The sequence variability is low. Up to now, three genotypes are detected (genotype 1-3 ), which occur in different regions of the world.
Biological Significance
Parvovirus B19 is the causative agent of fifth disease (erythema infectiosum ). Due to a life- long persistence of the infection immunity, the disease often occurs in children. Parvovirus B19 replicates exclusively in the erythroblasts, the progenitors of red blood cells (erythrocytes ) in the bone marrow. Therefore, the infection triggers a transient anemia, which can lead to complications and even death in immunocompromised or already anemic patients who can be treated by blood transfusions but timely. Patients who participated in a Änamie already before infection with parvovirus B19 - for example sickle cell anemia - suffer, have an increased risk of aplastic crisis. Even in pregnancy may cause spontaneous abortion and other complications such as fetal hydrops, which can cause serious harm to the fetus if it is not recognized.
After an infection with parvovirus B19, there is a very high viremia with virus concentration from 1012 to 1014 genomes / ml blood, the viruses are also in saliva and urine present. However, the symptoms set with a delay in the course of the immune response. The formation of antibodies and immune complexes causing so many so-called Acute symmetrical polyarthropathy, a painful joint inflammation. After this first phase, with high virus titers follows in some people, a second phase, in which the infection may enter into a permanent ( persistent ) state. The viral load is then 102 to 104 particles / ml blood is much lower, but then the viruses infect other target cells such as lymphocytes, macrophages, synovial cells, endothelial cells and tissues, such as heart, liver and skin. The inclusion of the viruses are likely to be overly antibodies original receptors play a significant role.
The genomes of viruses are a life long local limited detectable in these patients in parts of the skin, tonsils, myocardium and other tissues, but not infectious particles. Reactivation of the virus may be possible but not yet proven. Longer past infections can be detected by the presence of antibodies to the structural proteins VP1 and VP2. The number of seropositive people above the age of 65 years is about 70%.
Seroprevalence in Germany
Swell
- Heegaard ED, KE Brown: Human parvovirus B19. Clin Microbiol Rev (2002 ) 15 ( 3): pp. 485-505 PMID 12,097,253th